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    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
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    <title>Document</title>
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<body>
    <script>
    // 编写函数，求圆的面积
    function fn(a){
        yuan = a*a*3.14;
        document.write(`圆的面积为${yuan}`);
        
    }
    fn(prompt("圆的半径是多少？"));




    </script>
</body>
</html>